Leverage cycle stealing within optimization flows

ABSTRACT

A method, computer program product, and system for calculating an input timing slack at an input to a latch by subtracting an input arrival time to the latch from an input required arrival time, calculating an output timing slack at an output to the latch by subtracting an output arrival time of the latch from an output required arrival time from the latch, performing cycle stealing to improve the output timing slack by modifying the input required arrival time and the output arrival time, reducing the output timing slack by a pessimism amount, performing optimization in the integrated circuit to improve the input timing slack and the output timing slack, and increasing the output timing slack by the pessimism amount.

BACKGROUND

The present invention relates generally to a method, system, andcomputer program product for electronic design automation, and moreparticularly to a method, system, and computer program product for slackstealing improvement.

Electronic design automation (EDA) is used to design integratedcircuits. Integrated circuit or chip designers use EDA for analysis anddesign optimization of a semiconductor chip design. Analysis of thesemiconductor chip design includes timing analysis, which can providemeasurements of slack times of transparent latches in the semiconductorchip design. Design slack improvement can be performed by slackstealing, cycle stealing, or cycle steal adjusts, which will moveavailable slack from either an input or output side of a latch orelectrical component to another output or input of the component, bydesign adjustments to modify a clock launch and/or a data line arrivaltime.

Slack time can be defined as an amount of time a task can be delayedwithout causing another task to be delayed or impacting the completiontime of an electrical circuit design. Slack time, or slack, is adifference between a desired time or required time for a timing path andan achieved time or arrival time for the timing path. When an input to alatch arrives later than desired, this results in a negative inputslack, or the desired time is before the achieved time. A negative slackmeans that a data signal is unable to traverse Boolean or combinationallogic between a start point and an endpoint of a timing path fast enoughto ensure an electrical circuit functions as designed. Alternatively,when an input to the latch arrives sooner than desired, this results ina positive input slack, or the achieved time is before the desired time.An arrival time is the latest or earliest time at which an electricalsignal output from the latch may switch at a given location within thedesign. When an input or output on a latch is available later thandesired, this results in a negative input/output slack, and when theinput/output on the latch is available sooner than desired, this resultsin a positive input/output slack.

SUMMARY

Embodiments of the present invention disclose a method, a computerprogram product, and a computer system for calculating an input timingslack at an input to a latch by subtracting an input arrival time to thelatch from an input required arrival time, calculating an output timingslack at an output to the latch by subtracting an output arrival time ofthe latch from an output required arrival time from the latch,performing cycle stealing to improve the output timing slack bymodifying the input required arrival time and the output arrival time,reducing the output timing slack by a pessimism amount, performingoptimization in the integrated circuit to improve the input timing slackand the output timing slack, and increasing the output timing slack bythe pessimism amount.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1 is a functional block diagram illustrating a distributed dataprocessing environment, in accordance with an embodiment of the presentinvention;

FIG. 2 is a block diagram depicting leverage cycle stealing withinoptimization flows, in accordance with an embodiment of the presentinvention;

FIGS. 3A, 3B, 3C, 3D, 3E, and 3F, are each a timing diagram, inaccordance with an embodiment of the present invention;

FIG. 4 is a block diagram of internal and external components ofcomputers and servers depicted in FIG. 1, in accordance with anembodiment of the present invention;

FIG. 5 is a block diagram of functional layers of an illustrative cloudcomputing environment, including the distributed data processingenvironment depicted in FIG. 1, in accordance with an embodiment of thepresent invention; and

FIG. 6 is a functional block diagram of functional layers of theillustrative cloud computing environment of FIG. 5, in accordance withan embodiment of the present invention.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. In the description, details ofwell-known features and techniques may be omitted to avoid unnecessarilyobscuring the presented embodiments.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the interest of not obscuring the presentation of embodiments of thepresent invention, in the following detailed description, someprocessing steps or operations that are known in the art may have beencombined together for presentation and for illustration purposes and insome instances, may have not been described in detail. In otherinstances, some processing steps or operations that are known in the artmay not be described at all. It should be understood that the followingdescription is rather focused on the distinctive features or elements ofvarious embodiments of the present invention.

As previously described, electronic design automation (EDA) is used todesign integrated circuits. Integrated circuit or chip designers usethis software for analysis and design optimization of a semiconductorchip design. Analysis of the semiconductor chip design includes timinganalysis, which can provide measurements of slack times of electroniccomponents or transparent latches in the semiconductor chip design.Improvement of timing cycles can be performed by slack stealing or cyclestealing, which will move available slack from either an input or anoutput side of a latch to another side (output or input) of the latch,by adjusting a clock launch and data or test edge arrival side. Amicroprocessor electronic design of integrated circuits may havethousands of latches or transistors or electronic components.

The present invention generally relates to electronic design automationof integrated circuits. One way to improve electronic design automationis to leverage slack or cycle stealing by selectively adding temporarypessimism to select transparent latches, or latches. An embodiment bywhich to add temporary pessimism to select latches is described indetail below by referring to the accompanying drawings in FIGS. 1 to 6.Those skilled in the art will readily appreciate that the detaileddescription given herein with respect to these figures is forexplanatory purposes as the invention extends beyond these limitedembodiments.

Slack is considered ‘optimizable’ if there is improvement available inthe design above the current slack. Traditionally, cycle stealingalgorithms may measure slack, and perform timing adjustments based onthe available slack on the inputs or outputs of latches. The amount ofavailable slack is limited to the slack measurements and any positiveslack measurements, either at an input or at an output of a latch. Anoptimization tool may make design adjustments until the target ordesired or goal slack is achieved and/or available slack has beenrecovered to save power. A goal slack may be an output slack of zero, ora balanced input slack and output slack.

The input slack, T_(si), and the output slack, T_(so), may be calculatedfrom a deterministic (single corner) static timing analysis, may beprojected values obtained from a statistical timing run, may becanonical slacks from a statistical static timing analysis, may be fromsampling multiple deterministic static timing analysis, or may beobtained as a combination of slack values from multiple such analyses.

Referring now to FIG. 1, a functional block diagram illustrating asystem 100 in a networked computer environment, in accordance with anembodiment of the present invention, is shown. The system 100 mayinclude a client computer 102 and a server computer 104. The clientcomputer 102 may communicate with the server computer 104 via acommunications network 106 (hereinafter “network”). The client computer102 may include a processor 108, a data storage device 110, and isenabled to interface with a user and communicate with the servercomputer 104. The server computer 104 may also include a processor 112and a data storage device 114 that is enabled to run a temporarypessimism program 200. In an embodiment, the client computer 102 mayoperate as an input device including a user interface while thetemporary pessimism program 200 may run primarily on the server computer104. In an alternative embodiment, the temporary pessimism program 200may run primarily on the client computer 102 while the server computer104 may be used for processing a storage of data used by the temporarypessimism program 200.

It should be noted, however, that processing for the temporary pessimismprogram 200 may, in some instances be shared amongst the client computer102 and the server computer 104 in any ratio. In another embodiment, thetemporary pessimism program 200 may operate on more than one servercomputer 104, client computer 102, or some combination of servercomputers 104 and client computers 102, for example, a plurality ofclient computers 102 communicating across the network 106 with a singleserver computer 104.

The network 106 may include wired connections, wireless connections,fiber optic connections, or some combination thereof. In general, thenetwork 106 can be any combination of connections and protocols thatwill support communications between the client computer 102 and theserver computer 104. The network 106 may include various types ofnetworks, such as a local area network (LAN), a wide area network (WAN)such as the Internet, a telecommunication network, a wireless network, apublic switched network and/or a satellite network.

In various embodiments, the client computer 102 and/or the servercomputer 104 may be, for example, a laptop computer, tablet computer,netbook computer, personal computer (PC), a desktop computer, a personaldigital assistant (PDA), a smart phone, a mobile device, or anyprogrammable electronic device capable of communicating with the servercomputer 104 via the network 106. As described below with reference toFIG. 4, the client computer 102 and the server computer 104 may eachinclude internal and external components. In other embodiments, theserver computer 104 may be implemented in a cloud computing environment,for example, cloud computing nodes 510, as described in relation toFIGS. 5 and 6 below. Similarly, the client computer 102 may beimplemented in the cloud computing environment, for example, laptopcomputer 540C as shown in FIG. 5.

In an embodiment, the system 100 may include any number of clientcomputers 102 and/or server computers 104; however only one of each isshown for illustrative purposes only. It may be appreciated that FIG. 1provides only an illustration of an implementation and does not implyany limitations with regard to the environments in which differentembodiments may be implemented. Many modifications to the depictedenvironments may be made based on design and implementationrequirements.

The system 100 may be generally configured to perform actions toleverage slack or cycle stealing by selectively adding temporarypessimism to select latches of a circuit design. In this invention, theaddition of temporary pessimism creates incentives which allowoptimization to work beyond the goal slack such that more slack isavailable for an additional round of slack stealing, resulting in animproved overall design.

The temporary pessimism program 200, and associated methods aredescribed and explained in further detail below with reference to FIGS.2-6.

Referring now to FIG. 2 and with continued reference to FIG. 1, asimplified flow diagram of a temporary pessimism program 200 withinoptimization flows is provided, in accordance with an embodiment of thepresent invention. The temporary pessimism program 200 may be configuredto leverage slack or cycle stealing by selectively adding temporarypessimism to select latches of a circuit design. In an embodiment of thepresent invention, timing adjustments (or temporary pessimism) areselectively inserted in order to encourage optimization. Optimizationwith temporary pessimism may provide additional slack improvement at anoutput of select latches.

Timing analysis of an electronic circuit may be performed at step 202 ofthe temporary pessimism program 200. This timing analysis may calculateinput slack and output slack of each electronic device or latch in theelectronic circuit.

Referring now to FIGS. 3A-3F, and with continued reference to FIGS. 1and 2, FIGS. 3A-3F each have a timing diagram including a clock signal,an input signal, an output required time signal, and an output arrivaltime signal, in accordance with an embodiment of the present invention.In an embodiment, the clock signal and the input signal may be inputs toa first latch, while the output required time represents a requiredarrival time of an output of the first latch. The required arrival time,or input required arrival time, of the first latch is determined by theclock transition time as well as a corresponding setup time, as is shownas clock signal time in the following tables. The input as shown in theembodiment may be referred to as the input arrival time. This exampledemonstrates a late mode arrival time at the data input. The output ofthe first latch is input downstream to one or more additional latches inthe circuit, and the output required time is the worst required timefrom all downstream latches (as determined by timing analysis). Theoutput arrival time is the timing of the output of the first latchbefore feeding the downstream one or more additional latches in thecircuit.

An example of a timing analysis performed in step 202 of FIG. 2 is shownin FIG. 3A.

In the example of FIG. 3A, a late mode arrival time is considered fordata input to a latch, and an early mode arrival time is used for theoutput arrival time. In general, timing tests may include severalcombinations of early mode arrival time, late mode arrival time, earlymode of the output arrival time and late mode of the output arrivaltime. Input timing slack or input slack represents how the late modeinput or data signal on a latch is arriving relative to an early modeclock. For transparent latches, data may transition from data input tooutput at any time during the active interval of the clock (e.g., in theperiod of time between the clock rising and failing, for positive activelatches, and vice versa for negative active latches). However, to avoidloops in the timing graph, it is often advantageous in the process ofstatic timing analysis to select a cycle time boundary at some chosentime within the active clock interval. A loop in a timing graph is apath which feeds back to itself and should be avoided because acyclicstatic timing analysis would be unable to calculate signal arrivaltimes. A cycle boundary is a chosen time during the active interval ofthe clock by which data or input is required to arrive, and is also usedas a basis to compute a late mode output arrival time.

When an input data arrival time occurs at a latch after a chosen cycleboundary, or clock edge, a setup test failure (i.e., negative slack)will be reported. When an input data arrival time is before the cycleboundary, the slack at the input of the latch is positive. Output timingslack represents a worst slack for all paths feeding other end points(e.g., latches, or other timing nodes for which a constraint has beendefined) downstream from a latch, based upon the output arrival timeresulting from the chosen cycle boundary. By modeling the latch with aspecific cycle boundary time, static timing analysis is simplified inthat the timing propagation from data input to output can be removed andreplaced with a propagation time from clock to data output, occurring inconjunction with the chosen cycle boundary. This particular modelingapproach reduces the likelihood of problematic loops in the timing graphwhich would otherwise tend to occur when modeling the propagation ofdata from latch input to output.

In FIG. 3A, the clock signal changes from a low signal to a high signalat the time 100 picoseconds (ps). In this example, the desired time forthe input signal is at 100 ps, which is the time the clock signalchanges from a low signal to a high signal. The input signal changesfrom a low signal to a high signal at 105 ps. The resulting T_(si),input slack, is −5 ps, or 100 ps minus 105 ps, resulting in T_(si)=−5ps, which is the clock signal change time minus the input signal changetime. For exemplary purposes, latch setup time has been assumed to bezero in the present example, however those skilled in the art willreadily recognize that the slack at a latch input is dependent on latchsetup time as well. Furthermore, in this example, distinctions betweenlate and early arrival times are omitted, however those skilled in theart will readily recognize that timing values can be computed in eitherearly or late mode, and that slacks are generally computed by comparinga late mode data arrival time against an early mode clock, or viceversa. Also in this example, the output required time of the latchoutput, is computed to be 113 ps. The output arrival time of the latchoutput is available at 110 ps, demonstrated as a change from a lowsignal to a high signal at 110 ps. The output arrival time is before theoutput required time. The resulting T_(so) output slack, is 3 ps, or 113ps minus 110 ps, resulting in T_(so)=3 ps, which is the output requiredtime minus the output arrival time. A summary of the example slacktimings of FIG. 3A is shown below in Table 1, which also corresponds toan initial timing analysis, as performed in step 202 of the temporarypessimism program 200.

TABLE 1 Output Output Clock Input T_(si) required time arrival timeT_(so) 100 ps 105 ps −5 ps 113 ps 110 ps 3 ps

Referring back to FIG. 2, cycle stealing may be performed at step 204.Cycle stealing or slack stealing may move available slack from either aninput or output side of a latch or component to another output or inputof the component, by design adjustments to modify a clock launch and/ora data line arrival time. The purpose of cycle stealing is to determinean optimal or improved cycle boundary in the active interval of theclock period (e.g., between a rising clock edge and a falling clockedge, further adjusted by setup constraints), which ideally will reach agoal slack on both input and output. Input slack and output slack maynot completely be balanced by cycle stealing. Setup constraints are theextra time needed for a latch to capture the data input.

FIG. 3B demonstrates a resulting timing diagram of the clock signal, theinput signal, the output required time signal, and the output arrivaltime signal, after slack stealing. For example, there may be constraintsapplied to the cycle stealing algorithm to prevent the slack at theoutput of the latch from going negative as a result of a cycle stealingadjustment. In this example, after cycle stealing, the clock cycleboundary has been adjusted by 3 ps to a time of 103 ps, while the inputsignal changes from low to high at a time of 105 ps. The requiredarrival time for the input now is 103 ps. The input slack, T_(si) is −2ps, which is 103 ps minus 105 ps. This is an improvement of the inputslack. Previously the input slack was −5 ps, or the input signal wasavailable 5 ps after the cycle boundary which was originally assumed tobe coincident with the rising transition of the clock signal. Due toslack stealing, now the input slack is −2 ps, or the input signal isavailable 2 ps after the cycle boundary of the clock signal, which hasbeen adjusted by 3 ps. Slack stealing is also used to adjust the latchoutput arrival time by the same amount (3 ps) and the latch outputarrival time becomes 113 ps, which matches the required time for theoutput signal. The output changes from a low signal to a high signal at113 ps, and the output slack T_(si)=0 ps. Note that in this example, itis assumed that cycle stealing is constrained so as to prevent theintroduction of a negative slack at the latch output. A summary ofupdated slack timings of FIG. 3B after slack stealing is shown below inTable 2.

TABLE 2 Output Output Clock Input T_(si) required time arrival timeT_(so) 103 ps 105 ps −2 ps 113 ps 113 ps 0 ps

Referring back to FIG. 2, optimization may be performed at step 206. Anoptimization tool may calculate input slack and output slackmeasurements, make design changes to increase and decrease slack acrosseach electronic device in the electronic circuit, and recalculate inputslack and output slack after the design changes. This cycle may berepeated until design criteria is met or no further improvement isfound. Design criteria may include a slack goal of an output slack of 0,with any remaining slack on the input slack, or a balanced input slackand output slack.

In an example, a positive T_(so) can be reduced until it is 0, and thedesign adjustments made to a negative T_(si), to improve the T_(si) froma negative number to a less negative number, or to 0. Alternatively,design modifications may be made until T_(si) and T_(so) are equal, orbalanced. The slack goals may be dynamically set. The optimization toolmay be run by EDA software, or physical modeling synthesis. Theoptimization tool may also take into account total power consumption ofthe electronic circuit compared to targeted power consumption and howany design changes may affect power consumption, and also theperformance benefit of improved timings vs. power consumptionmodifications.

Design alterations to improve or increase slack may include increasing aphysical size of a logic device (for example an AND gate, an OR gate, aNOT gate, etc.) to make it larger, using a thicker wire, functionalswaps of design equivalents to make a design run faster, pin swappingand movement of electronic components closer physically in the circuit.Generally, an increase in circuit area, or an increase in powerconsumption or resources may be used to improve slack, for example alarger logic gate, and the transistors used to make the logic gate, willconsume more power or voltage, and use more physical space. Theoptimization tool may be used to modify the semiconductor chip design,recalculate the slack, and repeat design changes and slack measurements,until the slack reaches a goal, for example, a slack of 0. Typically,the optimization tool will stop working on a negative slack gate when itreaches the goal slack because pushing the slack above the goal may useadditional resources such as power and area.

Alternatively, design alterations to use available positive slack (andreduce power) include decreasing a physical size of a logic gate to makeit smaller, using thinner wire, functional swaps of design equivalentsto allow a portion of the design to run slower, pin swapping, andmovement of electronic components further apart physically in thecircuit design. These design alterations may be used to leverage otherdesign improvements which may improve slack in other areas of theelectrical component or device. A decrease in slack may correspond topower savings in the circuit or a reduction in power usage, or decreasephysical space of the circuit, and often will leave many latch outputslacks near a slack goal.

Referring back to the example shown in FIG. 3B and in Table 2 above, theoptimization step of step 206 of FIG. 2 would not do any further changesin the physical design of this example, because T_(so) is 0 ps, which isbe the design goal for this example, and no further design improvementswill be made. Thus, without this invention the input design slack wouldremain failing at T_(si)=−2 ps.

Timing adjustment may be performed at step 208 of FIG. 2. Timingadjustment includes adding temporary pessimism, or negative slack, toselect latches in the circuit, making output slack timings appear worse.The latches selected may be those which after an initial round of cyclestealing, one or more of the following conditions exist: an input slackremains negative or below a specified target value; input and outputslacks are not balanced; or a cycle boundary time (or clock time) chosenby the cycle stealing algorithm is before an end of an active intervalof the clock. As a result of the timing adjustment, the optimizationtool will then see a failing slack path on the output of latches whichit will attempt to improve by design changes, such as changing a wirelength or a wire thickness in a semiconductor chip design.

Note that in the above example of Table 2 or FIG. 3B, the first twoconditions have been met, specifically: an input slack remains negativeand the input and output slacks are not balanced. Furthermore, for anactive clock interval ending at time 110 ps, then the third condition ismet.

Temporary pessimism provides more available slack by forcing an outputslack measurement to be a lower value number, either a smaller positivenumber, 0, or a more negative number, making the output slackmeasurements appear to be failing by having a lower slack value and thusinduce the optimization tool to make design changes to improve the slackuntil it reaches the goal slack.

A determination of the amount of temporary pessimism to be added to anoutput of a latch may be done in multiple ways. In general, thispessimism will drive optimization to use additional physical area in thecircuit, and using alternate components which may increase power usage,in order to improve the slack. Thus, it is desirable to avoid addingpessimism that will not be used via slack stealing to improve the slackon the input of the latch. To avoid unnecessary optimization, themaximum pessimism added may be an amount of failing slack on the latchinput. Furthermore, the amount of additional available cycle stealing(i.e., the difference between the trailing edge of the clock and thecurrent cycle boundary) can be used as an upper bound on the amount oftemporary pessimism to apply on the output of a latch. This could befurther refined by attempting to assess how much slack improvement ispossible in a downstream circuit from the latch. A quick analysis of aworst downstream timing path could estimate how much slack could beimproved by using delay estimates. The delay estimates may use anexisting electronic circuit path transition time (time to switch fromhigh to low or low to high) and output capacitance, and determine thebest delay improvement found by using electronic components with a lowervoltage threshold or larger, stronger transistors. Output capacitance isthe ability of a design circuit to store electrical charge. A sum ofdelay improvements across all gates in a path could also be used tolimit the maximum pessimism added. A prior iteration of optimization maystore a maximum slack achievable on a particular latch, and may be usedas a possible maximum slack improvement. A score calculation comprisinga summation of a score with weights for different criteria may be usedto calculate a possible maximum slack improvement, and any pessimismadded should not exceed the possible maximum slack improvement.

In another example, the temporary pessimism may be universally appliedto an entire electronic circuit, or design. Power usage criteria for theelectronic design may also be taken into account, upon comparison with apower usage target.

Continuing with the example above of FIG. 3B and Table 2, and applyingtemporary pessimism to the latch, per the timing adjustment step 308 ofFIG. 2, resulting timings may be shown in FIG. 3C and summarized inTable 3 below. In this example, the output slack, T_(so), has beenadjusted. The other timings remain the same as in FIG. 3B. Note that incomparison to Table 2, the output arrival time has been modified by 2ps. The output arrival time has been changed from 113 ps to 115 ps,resulting in T_(so) of −2 ps. The output required time adjustment may beachieved as a result of modifying a delay value, modifying a timingadjustment, or modifying an output required time directly for a point ina downstream electrical signal fan-out cone from the latch.

TABLE 3 Output Output Clock Input T_(si) required time arrival timeT_(so) 103 ps 105 ps −2 ps 113 ps 115 ps −2 ps

Optimization may be performed at step 210 of FIG. 2. As described above,an optimization tool may calculate input slack and output slackmeasurements, make design changes to increase and decrease slack acrosseach electronic device in the electronic circuit, and recalculate inputslack and output slack after the design changes. Referring back to theexample shown in FIG. 3B and in Table 2 shown above, the optimizationstep 206 of FIG. 2 did not perform any further changes in the physicaldesign of this example, because T_(so) was 0. However, temporarypessimism has now been applied at step 208 of FIG. 2, and as shown inFIG. 3C and in Table 3 above, the T_(so) is now −2 ps. Therefore,optimization may be performed to further improve the slack timings inour example.

Continuing the example, after the optimization of step 210 of FIG. 2,updated slack timings are shown in FIG. 3D and Table 4 below. Designmodifications have resulted in an improved output required time changingfrom 113 ps to 115 ps, while the output arrival time remains at 115 ps.This modification has resulted in T_(so) improving from −2 ps to 0 ps.The addition of the temporary pessimism of step 208 has allowed theoptimization tool to continue with design improvements resulting in thisimprovement. The clock cycle boundary remains at 103 ps, the inputboundary remains at 105 ps, with the T_(si) remaining at −2 ps.

TABLE 4 Output Output Clock Input T_(si) required time arrival timeT_(so) 103 ps 105 ps −2 ps 115 ps 115 ps 0 ps

Timing adjustment removal may be done at step 212 of FIG. 2. This stepwill remove the temporary pessimism which was added at step 208.Continuing the example, −2 ps was added to T_(so) at step 208. In step212, 2 ps is added back to T_(so), resulting in a new value of T_(so) of2 ps, which is a positive value, indicating the output arrival time isbefore the output required time. Updated slack timings are shown in FIG.3E and Table 5 below.

TABLE 5 Output Output Clock Input T_(si) required time arrival timeT_(so) 103 ps 105 ps −2 ps 115 ps 113 ps 2 ps

Timing analysis with cycle stealing may be done at step 214 of FIG. 2.This is similar to steps 202 and 204 as described above. Any slackcreated on outputs during optimization can now be used by cycle stealingon failing inputs. In the example, the 2 ps of available slack on theoutput, T_(so), is available for the input slack, T_(si), which isfailing by 2 ps. Cycle stealing allows the clock cycle boundary to movefrom 103 ps to 105 ps, while the input remains at 105 ps. This resultsin T_(si) to be 0 ps. Cycle stealing has moved the output arrival timefrom 113 ps to 115 ps, while the output required time remains at 115 ps,resulting in T_(so) to be 0 ps. The overall slack for the input slack,T_(si), and the output slack, T_(so), in this example is now 0 psinstead of the previous best of −2 ps. The pessimism program 200 hasresulted in our circuit design now reaching the goal of T_(si)=0 ps andT_(so)=0 ps. Updated slack timings are shown in FIG. 3F and Table 6below.

TABLE 6 Output Output Clock Input T_(si) required time arrival timeT_(so) 105 ps 105 ps 0 ps 115 ps 115 ps 0 ps

Checking that slack timing goals of the circuit design can be done atstep 216 of FIG. 2. If the slack timing goals have not been met, thepessimism program 200 can continue to the timing adjustment step 208 ofFIG. 2. The pessimism program 200 may be repeated sequentially foradditional latches in the electronic circuit design, or the pessimismprogram 200 may be used for several latches at once. If the slack timinggoals have been met, the pessimism program 200 can continue to step 218.

Final power recovery may be performed at step 218. Final power recoverymay include removal of unnecessary slack created via the targetedpessimism which remains above the slack goal. The excess slack may beconsuming excess power, for example, if the input side of a latch hadalready achieved the slack goal and now is more positive or is now at anincreased positive slack. The excess slack can be reduced during powerrecovery operations, to reduce power usage of the circuit. For example,as described above, using a smaller size gate or a higher voltagethreshold for a component of the design or circuit may reduce powerusage of the circuit and may reduce excess slack.

Cycle stealing using optimization with pessimism allows for furtherrefinement of the circuit design, and improved overall slack, includingboth input slack and output slack of the electronic components orlatches in the circuit design. This allows for timing of the electronicdevices in the circuit design to be closer to desired timings orfrequency for the circuit design. The circuit design may be asemiconductor chip.

Referring now to FIG. 4, a block diagram of components of a computingdevice, such as the client computer 102 or the server computer 104, ofthe system 100 of FIG. 1, in accordance with an embodiment of thepresent invention is shown. It should be appreciated that FIG. 4provides only an illustration of an implementation and does not implyany limitations with regard to the environments in which differentembodiments may be implemented. Many modifications to the depictedenvironment may be made.

The computing device may include one or more processors 402, one or morecomputer-readable RAMs 404, one or more computer-readable ROMs 406, oneor more computer readable storage media 408, device drivers 412,read/write drive or interface 414, network adapter or interface 416, allinterconnected over a communications fabric 418. Communications fabric418 may be implemented with any architecture designed for passing dataand/or control information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system.

One or more operating systems 410, and one or more application programs411, for example, the temporary pessimism program 200, are stored on oneor more of the computer readable storage media 408 for execution by oneor more of the processors 402 via one or more of the respective RAMs 404(which typically include cache memory). In the illustrated embodiment,each of the computer readable storage media 408 may be a magnetic diskstorage device of an internal hard drive, CD-ROM, DVD, memory stick,magnetic tape, magnetic disk, optical disk, a semiconductor storagedevice such as RAM, ROM, EPROM, flash memory or any othercomputer-readable tangible storage device that can store a computerprogram and digital information.

The computing device may also include the R/W drive or interface 414 toread from and write to one or more portable computer readable storagemedia 426. Application programs 411 on the computing device may bestored on one or more of the portable computer readable storage media426, read via the respective R/W drive or interface 414 and loaded intothe respective computer readable storage media 408.

The computing device may also include the network adapter or interface416, such as a TCP/IP adapter card or wireless communication adapter(such as a 4G wireless communication adapter using OFDMA technology).Application programs 411 on the computing device may be downloaded tothe computing device from an external computer or external storagedevice via a network (for example, the Internet, a local area network orother wide area network or wireless network) and network adapter orinterface 416. From the network adapter or interface 416, the programsmay be loaded onto computer readable storage media 408. The network maycomprise copper wires, optical fibers, wireless transmission, routers,firewalls, switches, gateway computers and/or edge servers.

The computing device may also include a display screen 420, a keyboardor keypad 422, and a computer mouse or touchpad 424. Device drivers 412interface to display screen 420 for imaging, to keyboard or keypad 422,to computer mouse or touchpad 424, and/or to display screen 420 forpressure sensing of alphanumeric character entry and user selections.The device drivers 412, R/W drive or interface 414 and network adapteror interface 416 may comprise hardware and software (stored on computerreadable storage media 408 and/or ROM 406).

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

It is to be understood that although this disclosure includes a detaileddescription on cloud computing, implementation of the teachings recitedherein are not limited to a cloud computing environment. Rather,embodiments of the present invention are capable of being implemented inconjunction with any other type of computing environment now known orlater developed.

Cloud computing is a model of service delivery for enabling convenient,on-demand network access to a shared pool of configurable computingresources (e.g., networks, network bandwidth, servers, processing,memory, storage, applications, virtual machines, and services) that canbe rapidly provisioned and released with minimal management effort orinteraction with a provider of the service. This cloud model may includeat least five characteristics, at least three service models, and atleast four deployment models.

Characteristics of cloud computing include on-demand self-service, broadnetwork access, resource pooling, rapid elasticity, and measuredservice, which are each described below.

On-demand self-service: a cloud consumer can unilaterally provisioncomputing capabilities, such as server time and network storage, asneeded automatically without requiring human interaction with theservice's provider.

Broad network access: capabilities are available over a network andaccessed through standard mechanisms that promote use by heterogeneousthin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

Resource pooling: the provider's computing resources are pooled to servemultiple consumers using a multi-tenant model, with different physicaland virtual resources dynamically assigned and reassigned according todemand. There is a sense of location independence in that the consumergenerally has no control or knowledge over the exact location of theprovided resources but may be able to specify location at a higher levelof abstraction (e.g., country, state, or datacenter).

Rapid elasticity: capabilities can be rapidly and elasticallyprovisioned, in some cases automatically, to quickly scale out andrapidly released to quickly scale in. To the consumer, the capabilitiesavailable for provisioning often appear to be unlimited and can bepurchased in any quantity at any time.

Measured service: cloud systems automatically control and optimizeresource use by leveraging a metering capability at some level ofabstraction appropriate to the type of service (e.g., storage,processing, bandwidth, and active user accounts). Resource usage can bemonitored, controlled, and reported, providing transparency for both theprovider and consumer of the utilized service.

Service Models include Software as a Service, Platform as a Service, andInfrastructure as a Service, which are each described below.

Software as a Service (SaaS): the capability provided to the consumer isto use the provider's applications running on a cloud infrastructure.The applications are accessible from various client devices through athin client interface such as a web browser (e.g., web-based e-mail).The consumer does not manage or control the underlying cloudinfrastructure including network, servers, operating systems, storage,or even individual application capabilities, with the possible exceptionof limited user-specific application configuration settings.

Platform as a Service (PaaS): the capability provided to the consumer isto deploy onto the cloud infrastructure consumer-created or acquiredapplications created using programming languages and tools supported bythe provider. The consumer does not manage or control the underlyingcloud infrastructure including networks, servers, operating systems, orstorage, but has control over the deployed applications and possiblyapplication hosting environment configurations.

Infrastructure as a Service (IaaS): the capability provided to theconsumer is to provision processing, storage, networks, and otherfundamental computing resources where the consumer is able to deploy andrun arbitrary software, which can include operating systems andapplications. The consumer does not manage or control the underlyingcloud infrastructure but has control over operating systems, storage,deployed applications, and possibly limited control of select networkingcomponents (e.g., host firewalls).

Deployment Models include private cloud, community cloud, public cloud,and hybrid cloud, which are each described below.

Private cloud: the cloud infrastructure is operated solely for anorganization. It may be managed by the organization or a third party andmay exist on-premises or off-premises.

Community cloud: the cloud infrastructure is shared by severalorganizations and supports a specific community that has shared concerns(e.g., mission, security requirements, policy, and complianceconsiderations). It may be managed by the organizations or a third partyand may exist on-premises or off-premises.

Public cloud: the cloud infrastructure is made available to the generalpublic or a large industry group and is owned by an organization sellingcloud services.

Hybrid cloud: the cloud infrastructure is a composition of two or moreclouds (private, community, or public) that remain unique entities butare bound together by standardized or proprietary technology thatenables data and application portability (e.g., cloud bursting forload-balancing between clouds).

A cloud computing environment is service oriented with a focus onstatelessness, low coupling, modularity, and semantic interoperability.At the heart of cloud computing is an infrastructure that includes anetwork of interconnected nodes.

Referring now to FIG. 5, illustrative cloud computing environment 500 isdepicted. As shown, cloud computing environment 500 includes one or morecloud computing nodes 510 with which local computing devices used bycloud consumers, such as, for example, personal digital assistant (PDA)or cellular telephone 540A, desktop computer 540B, laptop computer 540C,and/or automobile computer system 540N may communicate. Cloud computingnodes 510 may communicate with one another. They may be grouped (notshown) physically or virtually, in one or more networks, such asPrivate, Community, Public, or Hybrid clouds as described hereinabove,or a combination thereof. This allows cloud computing environment 500 tooffer infrastructure, platforms and/or software as services for which acloud consumer does not need to maintain resources on a local computingdevice. It is understood that the types of computing devices 540A-Nshown in FIG. 5 are intended to be illustrative only and that cloudcomputing nodes 510 and cloud computing environment 500 can communicatewith any type of computerized device over any type of network and/ornetwork addressable connection (e.g., using a web browser).

Referring now to FIG. 6, a set of functional abstraction layers providedby cloud computing environment 500 (as shown in FIG. 5) is shown. Itshould be understood in advance that the components, layers, andfunctions shown in FIG. 6 are intended to be illustrative only andembodiments of the invention are not limited thereto. As depicted, thefollowing layers and corresponding functions are provided:

Hardware and software layer 660 includes hardware and softwarecomponents. Examples of hardware components include: mainframes 661;RISC (Reduced Instruction Set Computer) architecture based servers 662;servers 663; blade servers 664; storage devices 665; and networks andnetworking components 666. In some embodiments, software componentsinclude network application server software 667 and database software668.

Virtualization layer 670 provides an abstraction layer from which thefollowing examples of virtual entities may be provided: virtual servers671; virtual storage 672, for example the data storage device 114 asshown in FIG. 1; virtual networks 673, including virtual privatenetworks; virtual applications and operating systems 674; and virtualclients 675.

In an example, management layer 680 may provide the functions describedbelow. Resource provisioning 681 provides dynamic procurement ofcomputing resources and other resources that are utilized to performtasks within the cloud computing environment. Metering and Pricing 682provide cost tracking as resources are utilized within the cloudcomputing environment, and billing or invoicing for consumption of theseresources. In an example, these resources may include applicationsoftware licenses. Security provides identity verification for cloudconsumers and tasks, as well as protection for data and other resources.User portal 683 provides access to the cloud computing environment forconsumers and system administrators. Service level management 684provides cloud computing resource allocation and management such thatrequired service levels are met. Service Level Agreement (SLA) planningand fulfillment 685 provide pre-arrangement for, and procurement of,cloud computing resources for which a future requirement is anticipatedin accordance with an SLA.

Workloads layer 690 provides examples of functionality for which thecloud computing environment may be utilized. Examples of workloads andfunctions which may be provided from this layer include: mapping andnavigation 691; software development and lifecycle management 692;virtual classroom education delivery 693; data analytics processing 694;transaction processing 695; and leverage cycle stealing program 696. Theleverage cycle stealing program may improve slack timings of anelectronic circuit design.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general-purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. A computer program product for implementingtiming adjustments in an integrated circuit, the computer programproduct comprising: one or more computer-readable storage media andprogram instructions stored on the one or more computer-readable storagemedia, the program instructions comprising: program instructions tocalculate an input timing slack at an input to a latch by programinstructions to subtract an input arrival time to the latch from aninput required arrival time of the latch; program instructions tocalculate an output timing slack at an output to the latch by programinstructions to subtract an output arrival time of the latch from anoutput required arrival time from the latch; program instructions toperform cycle stealing to improve the output timing slack by programinstructions to modify the required arrival time of the latch and therequired output arrival time; program instructions to reduce the outputtiming slack by a pessimism amount; program instructions to performoptimization by program instructions to make design modifications in theintegrated circuit to improve the input timing slack and the outputtiming slack until a desired slack goal is achieved; and programinstructions to increase the output timing slack by the pessimismamount.
 2. The computer program product according to claim 1, furthercomprising: program instructions perform final power recovery.
 3. Thecomputer program product according to claim 1, wherein the latchcomprises at least one of the following: an unbalanced input timingslack and output timing slack, the output timing slack above a targetthreshold, or a cycle boundary occurring earlier than an end of anactive clock interval.
 4. The computer program product according toclaim 1, wherein program instructions to perform optimization comprisesat least one of the following: program instructions to modify a physicalsize of a logic device in the integrated circuit; program instructionsto change a wire size in the integrated circuit; and programinstructions to swap design equivalents.
 5. The computer program productaccording to claim 1, wherein the desired slack goal comprises theoutput timing slack equal to zero.
 6. The computer program productaccording to claim 1, wherein the desired slack goal comprises the inputtiming slack equal to the output timing slack.
 7. A computer system forimplementing timing adjustments in an integrated circuit, the computersystem comprising: one or more computer processors, one or morecomputer-readable storage media, and program instructions stored on theone or more computer-readable storage media for execution by at leastone of the one or more processors, the program instructions comprising:program instructions to calculate an input timing slack at an input to alatch by program instructions to subtract an input arrival time to thelatch from an input required arrival time of the latch; programinstructions to calculate an output timing slack at an output to thelatch by program instructions to subtract an output arrival time of thelatch from an output required arrival time from the latch; programinstructions to perform cycle stealing to improve the input timing slackby program instructions to modify the input required arrival time of thelatch and the output arrival time; program instructions to reduce theoutput timing slack by a pessimism amount; program instructions toperform optimization by program instructions to make designmodifications in the integrated circuit to improve the input timingslack and the output timing slack until a desired slack goal isachieved; and program instructions to increase the output timing slackby the pessimism amount.
 8. The computer system according to claim 7,further comprising: program instructions perform final power recovery.9. The computer system according to claim 7, wherein the latch comprisesat least one of the following: an unbalanced input timing slack andoutput timing slack, the output timing slack above a target threshold,or a cycle boundary occurring earlier than an end of an active clockinterval.
 10. The computer system according to claim 7, wherein programinstructions to perform optimization comprises at least one of thefollowing: program instructions to modify a physical size of a logicdevice in the integrated circuit; program instructions to change a wiresize in the integrated circuit; and program instructions to swap designequivalents.
 11. The computer system according to claim 7, whereinprogram instructions to perform final power recovery comprises: programinstructions to remove unnecessary output timing slack improvement; andprogram instructions to remove unnecessary input timing slackimprovement.
 12. The computer system according to claim 7, wherein thepessimism amount is based on at least one of the following: the inputtiming slack; program instructions to estimate a maximum possible slackimprovement; and program instructions to calculate a difference betweena current cycle boundary time and a time which corresponds with an endof an active clock interval.